Intensity control for crt display



Oct. 14., 1969 R. KOLODNYCKIJ 3,473,082

INTENSITY CONTROL FOR CRT DISPLAY Filed Sept. 20, 1968 Sheets-Sheet IOl4 DISPLAY PROCESSOR CONTROL --36 SHIFT REGISTER 221 ,52 24 y se MANUAL4 TRANSISTOR DELAY LINE WITH I INTENSITY SWITCHING TRANSMISSION CONTROLNETWORK DRIVERS 1 V NODE l 1 Vi WEIGHTED INPUT RESISTOR NETWORK V V2 2 2J! l iNODE REE AUTOMATICALLY VARlABLE FEEDBACK NETWORK V4 L uooz 4BLANK/UNBLANK 42 l CATHODE vomes v 44 CONTROL L Noose J POWER Fig.

. INVENTOR ROMA/V K OLOD/V YCK/J Oct. 14, 1969 R, KQLODNYCKIJ 3,473,082

INTENSITY CONTROL FOR CRT DISPLAY Filed se t.,20, 1968 Sheets-Sheer TUBEl TUBE 2 so- GRID so -o. DRIVE LIGHT OUTPUT FT. LAMBERTS 40d EXTINCTIONVOLTAG E TINCT ON VOLTAGE h l l 0 IO 20 3 0 40 5O 6O v K, VOLTS QUADRANTI QUADRANT 2 I l I .\I I FT. LAMBERTS: 40 FT. LAMBERTS JUADRKNT 3 QUXDRANT 4 20 FT. LAMBERTS IO FT. LAMBERTS Fig. 3

Oct. 14, 1969 R. KOLODNYCKIJ 3,473,032

INTENSITY CONTROL FOR CRT DISPLAY Filed Sept. 20, 1968 5 Sheets-Sheet06L 9 R. KOLODNYCKIJ 7 3,473,032

INTENSITY CONTROL FOR CRT DISPLAY Filed Sept. 20, 1968 5 Sheets-SheetUnited States Patent US. Cl. 315-30 Claims ABSTRACT OF THE DISCLOSURE Animproved image intensity control circuit for use with cathode ray tubedisplay is described. The intensity control system described providesfor permitting the changing of the intensity of n gradationsdifferentiated by a factor of 2, while permitting the intensities ofimages in different portions of the screen to be different with respectto other selected portions of the screen. The image intensity controlcircuit responds to externally applied digital-data intensity-definingsignals for providing the selected image intensity of the displayedimage automatically. An auxiliary manual intensity control device isdescribed for selecting a base level of intensity for use in conjunctionwith the externally applied digital-data intensity-defining signals. Theimage intensity control circuit operates to control the cathode-to-gridbias voltage for controlling the intensity of the electron beam.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates generally to the field of cathode ray tube displays, and hasparticular application for those cathode ray tube display devices havingcapability of dis playing vectors and characters. The invention isparticularly applicable to those cathode ray tube display devices thatare utilized in data processing systems.

Description of the prior art Prior art cathode ray tube display deviceshave had several problems in the control of the beam intensity, Oneproblem has been in arriving at a linear approximation of therelationship between the resulting intensity of the electron beam basedon the bias voltage applied to the cathode ray tube. Such non-linearityprovides the disadvantage of having the intensity change by diiferingamounts for incremental changes in the bias voltage. Another problem inthe prior art was the lack of the ability for a given image intensitycontrol circuit to respond to a plurality of programmable levels ofintensity as determined by a programmable control device such as thedata processor. While cathode ray tube display devices have beendeveloped that will provide for one or two image intensity levels, noknown prior art display systems have been made capable of providingprogrammable image intensity levels, nor have they provided for an imageintensity control circuit that will allow selected images or portions ofthe face of the cathode ray tube to exhibit different image intensities.While the prior art display devices have provided one form or another ofmanual intensity control, there are no known prior art devices thatcombine a programmable image intensity level control with a manualintensity control, whereby the entire display can be manually altered inintensity while maintaining the programmable difference of imageintensity of selected images. Yet another problem of the prior art, is

3,473,082 Patented Oct. 14, 1969 the matching of the response of beamdeflection system with the image intensity control circuit response.

SUMMARY With the foregoing mentioned problems of the prior art in mind,and with the object of providing an overall improved image intensitycontrol circuit, the subject invention was made. The image intensitycontrol circuit of this invention includes a cathode ray tube displaycontrol portion for receiving programmable commands from an associatedprocessor. The cathode ray tube control portion provides the overallcontrol for the cathode ray tube device, and provides the digital imageintensity control signals that are utilized to drive the image intensitycontrol circuit. Ultimately, the digital image intensity control signalsare converted to a voltage level by the image intensity control circuit,and applied to grid number 1 of a cathode ray tube for establishing acathode-to-grid bias voltage that will determine the image intensity ofthe light output from the cathode ray tube, The image intensity controlcircuit utilizes a transistor switching network at the input forreceiving the digital image intensity signals for driving a weightedinput resistor network for developing current levels to an amplifier.Associated with the amplifier is an automatically variable feed backnetwork that responds to the various current level inputs forcontrolling the voltage change at the output of the amplifier. A controlamplifier responds to this voltage and to a blank/unblank signal forproviding a resultant bias voltage to grid 1 of the cathode ray tubewhen the control amplifier is unblanked. A manual intensity controlcircuit is coupled to the transistor switching network for providing auniform bias level for the images on the entire face of the cathode raytube.

In view of the foregoing, it can be seen that a primary object of thisinvention is to provide an improved cathode ray tube display system. Yetanother object of this invention is to provide an improved imageintensity control circuit capable of responding to programmabledigitaldata intensity-defining signals for establishing programmablyalterable image intensity levels on the screen of the cathode ray tube.Still a further objective of this invention, is to provide an imageintensity control system for controlling the image intensity in acontinuous manner in response to digital-data intensity-defining inputsignals. Yet a further objective of this invention is to provide animproved image intensity control circuit wherein the over-all imageintensity can be manually controlled while maintaining programmedimage-intensity differences in the same ratios. Still a furtherobjective of this invention, is to provide an improved image intensitycontrol circuit utilizing a plurality of weighted input resistors inconjunction with an amplifier and an automatically variable feed backnetwork for providing digital-to-analog conversion for providing acontrolled cathode-to-grid bias voltage for a cathode ray tube.

BRIEF DESCRIPTION OF THE DRAWINGS grammable intensity levels arepresented as factors of 3 two in the four quadrants of the face of thecathode ray tube; and FIGURES 4a through 4c, when arranged as shown inFIGURE 4 are a circuit schematic diagram of the inventive imageintensity control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT In modern day cathode ray tubedisplay systems, it has been found desirable to intensify one or moreimages that appear on the face of the cathode ray tube to emphasize theimage by causing it to appear more brightly. The image intensity controlcircuit of this invention provides for changing the intensity of theimage to n gradations diiferentiated by the factor of two as well aspermitting different images to be different in intensity with respect toeach other. For example, referring briefly to FIGURE 3, it can be seenthat this system has been established wherein each quadrant isilluminated to a different degree, for example, when quadrant one isilluminated to 80 foot lamberts, quadrant two can be illuminated to 40foot lamberts, quadrant 3 to 20 foot lamberts, and quadrant 4 to footlamberts. In the drawing, image intensity is depicted by correspondinglyheavier lines. To accomplish the variable image intensity, imageintensity control circuitry is utilized to respond to digital-dataimage-intensity control signals for generating an appropriatecathode-to-grid bias voltage for the cathode ray tube. Referring to thisbias voltage as V it will be apparent that the image intensity I will bea function of the bias voltage V Therefore, by appropriately controllingthe bias voltage V the intensity I of the images on the cathode ray tubeface will be controlled.

Turning now to a consideration of FIGURE 1, which is a block diagram ofthe image intensity control circuit of this invention, there is shown adigital data processor 10 for providing control signals over path 12 tothe display control 14 of the cathode ray tube display device. Thesignals provided by processor 10 will include the designation of vectoror character images that are to be displayed on the cathode ray tube 16.Also, the processor will at least in part determine the intensity levelsto be applied to the cathode ray tube 16. The display control 14 willoperate to evaluate the signals received from processor 10 and willprovide further manipulation of the digital-data image-intensity controlsignals. It will be noted that in some cathode ray tube display devices,fixed time-increments are provided for displaying images of varyinglengths and sizes. Accordingly, in order for the various images toappear at uniform intensity, it is necessary to increase the biasvoltage V for the time interval that a relatively long vector image isto be displayed, over the level of the bias voltage V that would berequired for a shorter vector image. This factor is taken into accountby the display control 14 as one element in the determination of thedigital image-intensity control signals. Yet another factor indetermining the image intensity, is the intensity level specified by theprocessor 10. Taking all of the various factors required for thedetermination of the image intensity for any given image into account,the display control 14 sends a grouping of digital image-intensitycontrol signals over lines 18 to shift register 20. The shift register20 is then controlled by the display control 14 for providing theappropriate digital numerical value for input to the image intensitycontrol circuit. For sake of definition, it will be assumed that apredetermined minimum image intensity will result with the digitalimage-intensity control signals in an unshifted position in shiftregister 20. In order to change the intensity by a factor of 2, thedigital image-intensity control signals are shifted upward insignificance one position in order of magnitude. It will be understoodthat this relationship of a factor of 2 is purely arbitrary and thatdifferent gradations can be achieved by adjusting the circuitry in theimage intensity control circuit such that the relationship of theshifting in the shift register will have some other predeterminedrelationship to a change of intensity of the image on the face of thecathode ray tube 16.

The digital image-intensity control signals held in the shaft register20 are then applied over lines 22 to respective stages of a transistorswitching network 24. The combination of digital image-intensity controlsignals will cause selected ones of the transistor switches in thetransistor switching network 24 to switch and drive currents throughrespectively associated weighted input resistors in weighted inputresistor network 26. The weighted input resistor network 26 drives node2, which is coupled to an input of a high input-impedance amplifier 28,and node 2 will be seen to be a virtual ground. The weighted inputresistor 26 will determine the current flow at node 2. The summedcurrent of node 2 is also applied to the automatically variable feedback network 32. The amplifier 28 receives a reference level 30 and iscoupled to the automatically variable feedback network 32. Theautomatically variable feedback network 32 sees the same current flowfrom the summing resistors as the high inputimpedance amplifier 28. Asdifferent current increments are provided in response to differentselections made by the digital image-intensity control signals, theimpedance of the automatically variable feedback network 32 will bevaried. The interaction of the automatically variable feedback network32 and amplifier 28 will determine the potential V4 at node 4.

The potential V4 is applied to the control amplifier 34. This controlamplifier also receives the blank/unblank control signal from thedisplay control 14 by way of control line 36, the delay line withtransmission drivers 38, and control line 40. If the potential at node 4is higher than the potential V5 at node 5, the potential V6 at node 6will be driven accordingly. The potential V6 at node 6 in combinationwith a potential at the cathode K of the cathode ray tube determine Vthe tube bias. To blank the tube, the display control 14 provides asignal through the delay line transmission drivers 38 for holding thepotential V5 more positive than the potential V4. To unblank the cathoderay tube, potential V5 is dropped below the level of V4 and the image isunblanked and allowed to establish a bias at node 6 that will cause theimage to be displayed. A cathode voltage control 42 is coupled via line44 to the cathode K of tube 16. Tube 16 also has power source 46 coupledto grid G2 via line 48 and to tube via line 50. As will be described inmore detail below, the delay line with transmission drivers 38, isutilized to synchronize the deflection signals and the image intensitysignals.

It will be recalled that the voltage V1 at node 1 basically determinesthe ultimate image intensity by controlling the voltage applied to gridG1. A manual intensity control 52 is coupled to a voltage source V anddirected over line 54 to the transistors switching network 24. Themanual intensity control 52 operates to establish a base level of imageintensity. By way of example, let it be assumed that the manualintensity control 52 is at a predetermined image intensity level. Thedisplay control 14 then provides shifted digital image intensity controlsignals to the transistor switching network 24, whereby the image willbe displayed at foot lamberts. Then let it be assumed that another imageis displayed by the display control 14 at 40' foot lamberts, with thesame manual intensity control setting. The system is so arranged thatunder these conditions, changing the manual intensity control 52 suchthat the 80 foot lambert image is displayed at 60 foot lamberts, thesecond image will be correspondingly reduced in illumination to maintainthe same illumination ratio. Therefore it can be seen that for anycombination of intensities of images, the manual intensity control 52will operate to either increase or decrease the image intensity for theentire display.

Next turning to a consideration of FIGURE 2, it will be seen that it isa plot of the light output in foot lamberts for two cathode ray tubesbased on the cathode-to-grid voltage diiferentials. This figure isintended to show that different tubes will have different extinctionvoltages. In order to accommodate these different extinction voltagescharacteristics, a cathode voltage control 42 is utilized in the imageintensity control circuit of this invention. The adjustment is made toaccommodate the characteristic of the given tube and will be discussedin somewhat'more detail below in the consideration of the detailcircuitry.

Turning now to a consideration of FIGURES 4a through 4c, which whenarranged as shown in FIGURE 4, are a detailed circuit diagram of theimage intensity control circuit of this invention. The variouscomponents utilized in the preferred embodiment are set forth in TableI. It should be understood that these components are availablecommercially, and that while the particular circuit diagram shown hasbeen found to be advantageous in performing the desired functions, it isrecognized that various circuit modifications could be made withoutdeparting from the scope and spirit of the invention.

In this discussion, the circuit components that are included within theblock representations referred to in FIGURE 1 will be enclosed indashed-line blocks and will bear similar reference numerals. Referenceto the particular circuit components will be by way of specificcomponent reference designation.

The transistors switching network is shown enclosed within dashed block24, and for this embodiment comprises stages 2 through 2. These inputterminals are coupled to the shift register mentioned with regard toFIGURE 1. For this embodiment, ground (a substantial zero volt signal)will represent a logical 1; and a plus voltage (for example +6- volts),will represent a logical 0. The circuit arrangement is such each of thestages operate in a similar fashion, so a consideration of an examplestage will be suflicient for understanding of the circuit operation.Considering the lowest ordered stage for bit position 2, it will be seenthat transistor Q9 has a pair of matched diodes CR45a and CR45b coupledanode-toanode across the collector-emitter circuit of transistor Q9. Theselection of the resistor, capacitor, and diode values for the remainderof the circuit, as shown in Table I, and is such that when the digitalinput signal is such that transistor Q9 is switched to a conductingstate, the voltage at node 1 for the stage will be zero. Alternatively,if the digital input signal to the stage is such that transistor Q9 isswitched to a nonconducting state, the potential level at node 1 for thestage will be at a positive level. With the transistor Q9 switched toconduct, a portion of the current flow will be through resistor R27 andthe resistor to ground, at a portion will be through resistor R36 anddiode CR45b to ground. This will result, as mentioned above, insubstantially a zero voltage at node 1 for the stage. However, when thetransistor Q9 is switched off, the current flow will be partiallythrough resistor R36 and CR45b to ground, and partially through CR4-5ato node 1 and then to resistor R54.

The weighted input resistor network 26 is comprised of resistors R46through R54. These weighted resistors have a resistive valuerelationship of a power of 2. That is, R46 has a nominal resistor valueR. For this embodiment, the value R is of 9530 ohms. Resistor R47 istwice this value; R48 is four times this value; R49 is eight times thisvalue; R50 is sixteen times this value; R51 is thirtytwo times thisvalue; R52 is sixty-four times this value; R53 is one hundredtwenty-eight times this value; and R54 is two hundred fifty-six timesthis value. From this it can be seen that the least significant digitposition 2 has the largest resistor value and will provide the smallestincrement of current. Alternatively, stage'2 has the smallest resistivevalue and will provide the largest increment of current. These Weightedinput resistors are coupled to a common point and then to node 2 foramplifier A in the circuit diagram. The same common point is coupled asan input to the automatically variable feedback network 32.

The circuitry enclosed within dashed block 28, 30 comprises theamplifier 28 and the reference 30, referred to in FIGURE 1. In thiscircuitry representation the amplifier 28 is referred to as A, and theremainder of the circuitry is utilized to establish the reference forone of the inputs to the amplifier.

Amplifier A has a high input impedance. The summing resistors R46through R54 will determine the current fiow to node 2, as mentionedabove. This same current flow will be provided to the automaticallyvariable feedback network 32. This automatically variable network iscoupled across the amplifier A, and receives the same current flow asprovided at node 2. A voltage regulator, shown enclosed in dashed blck60, provides the regulated 12 volt level to the common point ofresistors R64 through R68. The summed current is provided to a commonpoint of diodes CR46, CR48 through CR52, and resistor R63. A commonpoint for resistors R63, R69 through R73, and diode CR47 is coupled toline common with node 4. The arrangement of diodes and resistors, asshown, results in an automatically variable resistive value for thetotal network that is dependent upon the current level applied thereto.That is, as additional increments of current are added by appropriatelyselecting higher valued digitaldata image-intensity defining signals,the total resistive value of the network will be altered. Therefore, thecombination of the automatically variable feedback network 32 and theamplifier circuit arrangement 28, 30 as controlled by the current levelin the summing resistors, will determine the potential V4 at node 4.

Node 4 is coupled as input to the control amplifier section, shownenclosed in dashed block 34. The control amplifier provides an output atnode 6 that is directed to grid 1 of the cathode ray tube. Controlamplifier 34 also receives th blank/unblanked control signal. Thecircuitry shown enclosed within dashed block 38 includes the delay linewith the transmission drivers and controls for the blanking andunblanking of the cathode ray tube in accordance with the signalreceived from the display control 14 at the diode CR107. The blank orunblank signal so applied, is passed through the amplifiers includingtransistors Q109 and Q110 and to a selected tap on the delay line, suchas the input tap to L2. Another selected tap is coupled to a terminal ofresistor R119 where the signal is utilized to drive another amplifierthat determines the voltage level at node 5. When the appropriateunblank signal is received at CR107, a predetermined time later,transistor Q10 is switched to saturation and operates to drivetransistor Q13 to a mode of operation for providing a voltage level atnode 5 lower than the voltage level at node 4. Under such a condition,the cathode ray tube is unblanked and the voltage level in controlamplifier 34, as determined by the current sum resulting from theweighted input resistor network 26, will be passed to the cathode raytube grid 1. Alternatively, when the blank signal is received at CR107,transistor Q10 will be switched off, and in turn, will cause Q13 to putnode 5 at a voltage level higher than the voltage level of node 4.

The delay line is utilized to match the propagation time for thedeflection amplifier to the image intensity control circuit.

It will be recalled from the consideration of FIGURE 2, that variouscathode ray tubes have different voltages ranges required for thecathode-to-grid bias to cause extinction. To accommodate varyingparameter tubes, the circuitry enclosed within dashed block 42 is usedfor providing a variable voltage drive to the cathode ray tube. It canbe seen that a voltage divider network comprised of resistors R87together with potentiometer R88 are coupled intermediate plus 24 voltand minus 24 volt supplies. It will be noted that 48 volts is the mostnegative that grid 1 can be driven. For those tubes requiring a greatervolt- 7 age diiference for the cathode-to-grid potential difference, thepotentiometer R88 can be adjusted to provide this necessary potentialdifference. These adjustments are normally made to accommodate the imageintensity control circuits to a particular tube.

The manual intensity control is shown enclosed in dashed block 52.. Themanual control, labeled MC, is provided at the operators console. Thismanual control is a potentiometer coupled between a ground level and +24volts. The wiper of the potentiometer is coupled to the input ofamplifier stage Q105 which in turn drives transistors Q106 and Q117. Thecollector of transistor Q117 is coupled to the common points of thecollectorresistors R19 through R27 for the transistor switching network24. This potential in conjunction with the ground potential coupled tothe emitter circuits provides the operational parameters for thetransistors switching network, and allow the intensity of images appliedon the cathode ray tube to be changed in intensity by the manipulationof control MC. As described above, the operation of the manual controlis over and above the operation that is provided by the application ofthe digital-data intensity-defining signals to the input terminals ofthe transistor switching network.

TABLE I 61 R1 through R9. gg through R18, R74" Capacitor, 75 V., 2.2uf.:20%. Resistor, 200 ohm 1%. Resistor, 750 ohm:1%. Resistor, 1,300ohm: 1%;

s or.

Resistor, 1,500 ohm:1%. Resistor, 200 ohm:2%. Resistor, 010 ohm:2%.Resistor, 1,050 ohm: 1%. Resistor, 1,150 ohm: 1%. Resistor, 1,240 ohm:1%. Resistor, 2,370 ohm 1%. Resistor, 5,110 ohm:1%.- Resistor, 11,800ohm 1% Resistor, 5,000 ohm: 1%. Resistor, 7,150 ohm:1%. Resistor, 9,530oh1n:l%. Resistor, 9,760 ohm: 1%. Resistor, 10,500 ohm 1%; Resistor,5,760 ohm:1%. Resistor, 19,100 ohrn='=1%. Resistor, 24,300 ohm: 1%.Resistor, 38,300 ohm:1%. Resistor, 61,900 ohm 1%. Resistor, 68,100ohm:l%. Resistor, 76,800: 1%. Resistor.

Do. Resistor, 1.5K ohm:2%. Resistor, 160 ohm:2%. Diode, VR, 1 watt, 15.0volt. Resistor, 160 ohm:%. Resistor, 510 ohm: 5%. Resistor, 3.0K ohm:5%.Resistor, 1.2K ohm 5%. Resistor, 45K ohm: 5%. Resistor, 430K ohm 5%.Resistor, 620K ohm 5%. Resistor, 1.2M ohm:5%. Resistor, 2.4M ohm:5%.Resistor, 240 ohm:i;2%. Capacitor, 35 volt, 2.2 pf. Diode, Zener, 12volt.

Resistor, 750 ohm 2%. Resistor, 16K ohm:2%. Resistor, 560 ohm:2%.Resistor, variable, 200 ohm: 10%;

C1 through 09, C14 CR1 through CR36, CR46 through OR56, CR59, CR60.CR62, CR63 through GR65 C16, 017, 020 CR3? through 01145-.

R117..." R125, R126- R127, R131- R132...

Resistor, variable, 5,000 ohm: 10%.

Resistor, variable, 1 megohm, :10%.-

Transistor, PNP.

Resistor, 2,320 ohm, :1%.

Capacitor, 1 cov, 100 L, :2%.

Diode, 250 mw., 40 v.

Diode, 250 mw., 40 v.

Capacitor, volt., .01 pf. :20%.

Diodes, matched dual-silicon.

. Transistor, NPN, switching, 360 mW., 40 v.

.... Transistor-NPN, 360 mw., 40 v.

Resistor, 12 ohm 2%.

Resistor, 200 ohm, =|;2%.

Resistor, 360 ohm 2%:

Resistor, 560 ohm 2%.

Resistor, 1.6K ohm:2%.

Resistor, 27K ohm 5%.

.. Delay line4 pH.

. Delay line1 H.

Resistor, 2.0K ohm:5%;

Resistor, 3.0K ohm:5%.

Capacitor, volt, 2.2 tF:20%.

Capacitor, 35 volt, 22 #F:20%.

Resistor, 300 ohm 2%.

Resistor, 750 ohm:2%.

Resistor, 16K ohm:2%.

Resistor, variable, 500 ohm, :10%.

Transistor, NPN, 360 mw., v.

Capacitor, v., 4,700 pf. 20%.

Transistor-PNP.

Capacitor, 100 volt, 25 13. :2%.

Capacitor, 100 v., 100 K, :2%.

Diode, 250 mw., 40 v.

Transistor-PNP, power.

Transistor, NPN, 360 mW., 40 V.

Resistor, 1.3K ohm 2%.

Resistor, 200 ohm, ='=5%.

Resistor, 300 ohm 5%.

Q .I. Transistor-NPN, 500 mW., on v.

9 SUMMARY From the foregoing description of the detailed circuitdiagram, and the discussion of the general circuit arrangement, it canbe seen that an improved image intensity control circuit has beendescribed for use with a cathode ray tube display system. The use of thetransistor switching network allows a display control to provideappropriately positioned digital-data intensity-defining signals forestablishing the predetermined programmable level of image intensity forany image that is being displayed. The image intensity can beprogrammably altered by shifting the digital-data intensity-definingsignals prior to their application to the transistor switching network.The weighted resistor network then provides a current sum that isutilized by the high input-impedance amplifier and the automaticallyvariable feedback network to provide a voltage level for driving thecontrol amplifier in a manner to change the bias voltage on grid 1 ofthe cathode ray tube. The manual intensity control operates to providecontrolled levels of intensity for the entire cathode ray tube.

Having then described a preferred embodiment of this invention, it beingapparent that various modifications will become apparent to thoseskilled in the art without departing from the spirit and scope of theinvention, what is intended to be protected by Letters Patent is setforth in the appended claims.

I claim:

1. An image intensity control circuit for use with a cathode ray tubedisplay device comprising:

switching means for receiving programmably alterable digital-dataimage-intensity defining signals;

weighted resistor network means coupled to said switching means forproviding current sums indicative of the intensity values of saiddigital-data image-intensity defining signals; automatically variableimpedance means coupled to said weighted resistor network means forproviding voltage levels in response to said current sums; and

output means coupled to said automatically variable impedance means forproviding bias voltages to a grid in a cathode ray tube in response tosaid voltage levels.

2. An image intensity control circuit as in claim 1 wherein saidswitching means includes a plurality of transistor-switch stages, eachof said stages including a transistor having emitter, collector, andbase electrodes, a pair of matched diodes having terminals coupled inopposed directions of current flow, one of said pair of matched diodeshaving another terminal coupled to said emitter electrode, and the otherof said pair of matched diodes having another terminal for coupling to afirst source of potential, said terminals coupled in common furthercoupled to load resistor means for coupling to a second source ofpotential, and resistor means coupled to said collector terminal forcoupling to a variable source of potential.

3. An image intensity control circuit as in claim 2 and furtherincluding variable potential means coupled to said resistor means ofeach of said stages for establishing a desired level of intensity ofimages displayed.

4. An image intensity control circuit as in claim 3 wherein saidvariable potential means includes manually operable control means forcoupling to a third source of potential for providing manuallyselectable potential levels to said resistor means, thereby establishingsaid desired level of intensity.

5. In image intensity control circuit as in claim 1 and furtherincluding manual intensity control means for providing manuallycontrolled levels of said bias voltages for controlling the intensity ofimages on said cathode ray tube in conjunction with said digital-dataimage-intensity defining signals.

6. An image intensity control circuit as in claim 1 and furtherincluding cathode control means for coupling to the cathode of saidcathode ray tube for controlling the potential on said cathode, thepotential on said cathode and said bias voltages determining theintensity of images on said cathode ray tube.

7. An image intensity control circuit as in claim 1 wherein said outputmeans includes blanking means having input means for alternativelyreceiving blanking and unblanking signals, said blanking means includingmeans for passing said bias voltage to said grid in response to saidunblanking signal and for preventing said bias voltage from passing tosaid grid in response to said blanking signal.

8. An image intensity control circuit as in claim 7 wherein saidblanking means includes signal delay means for synchronizing theapplication of said bias voltages to said grid with the operation ofdeflection circuits in the cathode ray tube display device.

9. An image intensity control circuit as in claim 1 wherein saidweighted resistor network means includes 11 resistor means havingresistive values for any 1 of said resistor means of 2 R, where R is apredetermined basic resistive value, 11 and i are integers, and each ofsaid resistor means is associated with a predetermined one ofdigital-data image-intensity defining signals.

10. An image intensity control circuit as in claim 1 wherein saidautomatically variable impedance means includes a high input-impedanceamplifier means having an output terminal and an input terminal coupledto said weighted resistor network means for receiving said current sums,reference means coupled to said high input impedance amplifier means,and automatically variable feedback network means having a first inputterminal for coupling to a source of regulated potential, a second inputterminal coupled to said weighted resistor network means for receivingsaid current sums, and output means coupled to said output terminal,said automatically variable feedback network means providing differinglevels of impedance in response to said current sums.

References Cited UNITED STATES PATENTS 3,004,187 10/1961 Olson 3l5223,336,587 8/1967 Brown 315-22 3,388,391 6/1968 Clark 31522 X 3,403,2919/1968 Lazarchick et al. 315-30 RODNEY D. BENNETT, 1a., Primary ExaminerHERBERT C. WAMSLEY, Assistant Examiner US. Cl. X.R. 315-22

